Enduring Understanding 3.A.1: Ionic and Net Ionic Equations

  • In solution, some ions will participate in a chemical reaction (e.g. forming a precipitate) while others will remain in solution, unchanged. These ions that are unchanged in a reaction are called spectator ions.
  • Sometimes, it is useful to remove spectator ions from chemical equations and just write equations with the species that actually react. These are called net ionic equations.

  • Example: The reaction of barium nitrate and sodium sulfate solutions to form a barium sulfate precipitate:
  • For the reaction: Ba(NO3)2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2NaNO3 (aq)
  • The full ionic equation of this reaction shows soluble ionic compounds as separate ions:
  • Ba2+ + 2 NO3- + 2 Na+ + SO42- → BaSO4 (s) + 2 Na+ + 2 NO3-
  • This is the complete ionic equation. Barium and sulfate ions react to form barium sulfate precipitate, and the sodium and nitrate ions are unchanged - they are spectator ions.
  • If we remove the unchanged ions from each side of the equation:
  • Ba2+ + 2 NO3- + 2 Na+ + SO42- → BaSO4 (s) + 2 Na+ + 2 NO3-
  • If we remove the unchanged ions from each side of the equation:
  • Ba2+ + SO42- → BaSO4 (s)
  • This is the net ionic equation, showing only the ions involved in the reaction.

  • Example 1: What are the spectator ions in the reaction of AgNO3(aq) and KCl(aq) to form an AgCl precipitate?
  • Ag+ and Cl- are forming the precipitate, so NO3- and K+ are the spectator ions.

  • Example 2: If a solution of sodium bicarbonate is mixed with hydrochloric acid, sodium chloride solution, carbon dioxide, and water are produced. What are the total and net ionic equations?
  • The total reaction equation is:
  • NaHCO3 (aq) + HCl (aq) → NaCl (aq) + CO2 (g) + H2O (l)
  • The total ionic reaction is:
  • Na+ + HCO3- + H+ + Cl- → Na+ + Cl- + CO2 (g) + H2O (l)
  • Na+ and Cl- are present unchanged on both sides of the equation. The net ionic reaction is therefore:
  • HCO3- + H+ → CO2 (g) + H2O (l)


Related Links:
Chemistry
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AP Chemistry Notes
Balanced Chemical Equations


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